Technical Abstract:
A relatively new starch product with various novel applications is a porous microcellular foam. The foam product is made by dehydrating a starch hydrogel in a solvent such as ethanol and then removing the solvent to form a foam product. The process involves heating an aqueous slurry of starch (8% w/w) in a reaction vessel to 140°C for 10 min. The melt temperature is lowered to 85°C and the melt is pumped through a spray nozzle. Atomized starch spheres are collected in a solution of 90% ethanol/water and dehydrated in ethanol. Particle size distribution of sprayed and homogenized particles was measured using a particle size analyzer and foam microstructure was observed using Scanning Electron Microscopy (SEM). Heating conditions used in the study effectively solubilized the starch granules to the point that no granule remnants were visible. Spray and homogenization methods were both effective in producing a fraction of starch particles in the desirable size range. Typical size distribution curves showed particle sizes ranging from 3 to 100 µm (Fig. 1). The spray technique yielded particles with a slightly higher mean value compared to the homogenized sample but differences were not significant (Table 1). Some of the larger sized particles appeared to be attributable to particle agglomeration (Fig. 2A). Sonication of starch samples helped reduce agglomeration and reduced particle size distribution. The starch particles had an open-cell matrix with pore sizes in the submicrometer range (Fig. 2B). The porous microcellular foam beads are currently being field tested in honeybee colonies.